Gotcha, I think my android friends are on messenger too so If I need to send them video or pdfs I useMessages works fine when you're messaging other iPhones - but if you need a cross platform chat that works as well as Messages you need a 3rd party app - which is why everyone in Europe is on Whatsapp, i'm not sure why this is so different in the US.
I don't personally like Whatsapp but I still have it for a few friends that are on Android and don't use any other apps - I also use Facebook messenger for other people but my app of choice would be Signal where i have specifically 3 friends who won't use Whatsapp and don't have iPhones.
that but between those two, I'm covered.